In a power supply circuit for an IC (Integrated Circuit) such as a CPU (Control Processing Unit) of a computer, high frequency noise is generated due to the high-speed processing of the IC. In light of this, a bypass capacitor for removing high-frequency noise from the power supply circuit is often provided in the power supply line for the IC. The bypass capacitor fulfills the decoupling function of preventing noise transmission from the power supply circuit to the IC and the stabilizing function of preventing the fluctuation of power supply voltage by temporarily supplementing or storing current when the load current changes largely. For such a bypass capacitor, use may be made of a ceramic capacitor or a tantalum capacitor.
Recently, with the speed increase of an IC, a bypass capacitor having a large capacitance, a low ESL (Equivalent Series Inductance) and a high responsibility is in demand. Also for a chip-type solid electrolytic capacitor using a sintered body of valve metal powder such as a tantalum capacitor, further decrease of the ESL is needed.
As compared with a chip ceramic capacitor, to increase the capacitance of a solid electrolytic capacitor is relatively easy. However, in a conventional chip-type solid electrolytic capacitor, the capacitor element, which substantially acts as a capacitor, is enclosed in a resin package, and this requires leads for connecting the anode and the cathode of the capacitor element to an anode terminal and a cathode terminal provided outside the resin package. These leads, however, result in an equivalent series inductance (ESL), thereby putting a limitation on the amount of decrease in the ESL of conventional chip-type solid electrolytic capacitors.
FIG. 19 is a sectional view showing a conventional solid electrolytic capacitor configured to be mounted on the surface of a printed board.
The illustrated solid electrolytic capacitor 100 includes a capacitor element 101 in a prismatic form enclosed in a resin package 107 in the form of a rectangular parallelepiped. The lower surface 107c of the resin package 107 is the mount surface to be mounted on a printed board. The resin package 107 may be about 2 to 3 mm in length (lateral dimension in FIG. 19), about 1 to 2 mm in width, and about 1 to 2 mm in height. The mounting electrode (the end 105c of an anode terminal 105 and the end 106c of a cathode terminal 106 in FIG. 19), which is formed on the lower surface 107c of the resin package 107, may be about 0.8 mm in length (lateral dimension in FIG. 19).
The capacitor element 101 comprises a prismatic porous sintered body 102 made of valve metal, an anode wire 103 of about 0.2 mm in diameter partially embedded at the substantial center of a side surface 102a of the porous sintered body 102, and a metal layer 104 serving as a cathode (hereinafter referred to as a cathode 104 when necessary) and formed on surfaces other than the side surface 102a. The region between the portion of the anode wire 103 which is located within the porous sintered body (hereinafter, this portion is referred to as an anode 103a) and the cathode 104 functions as a capacitor.
To the portion 103b of the anode wire 103 which projects from the porous sintered body 102, the anode terminal 105 made of a conductive material and channel-shaped in section is connected to guide the anode 103a to the lower surface 107c of the resin package 107. To the metal layer 104 on the upper surface of the capacitor element 101, the cathode terminal 106 made of a conductive material and channel-shaped in section is connected to guide the cathode (the entire metal layer 104) of the capacitor element 101 to the lower surface 107c of the resin package 107.
The base end 105a of the anode terminal 105 serves as a connecting portion for connection with the lead portion 103b of the anode wire 103, whereas the end 105c of the anode terminal 105 serves as a connecting portion (hereinafter referred to as mount portion) for connection with an electrode on the mount surface of the printed board by e.g. soldering. The intermediate portion 105b of the anode terminal 105 serves as a lead portion for guiding the anode 103a of the capacitor element 101 to the mount portion 105c on the lower surface 107c of the resin package 107.
Similarly, the base end 106a of the cathode terminal 106 serves as a connecting portion for connection with the cathode 104, whereas the end 106c of the cathode terminal 106 serves as a connecting portion (mount portion) for connection with an electrode on the mount surface of the printed board by e.g. soldering. The intermediate portion 106b of the cathode terminal 106 serves as a lead portion for guiding the cathode 104 of the capacitor element 101 to the mount portion 106c on the lower surface 107c of the resin package 107.
The lead portion 106b of the cathode terminal 106 is bent to be inclined at a region within the resin package 107. This is because, in forming the anode terminal 105 and the cathode terminal 106 using a lead frame, the position of the connecting portion 105a of the anode terminal 105 for connection with the anode wire 103 and the position of the connecting portion 106a of the cathode terminal 106 for connection with the cathode 104 are deviated from each other correspondingly to the height difference between the anode wire 103 and the cathode 104 of the capacitor element 101.
Each of the anode terminals 105 and the cathode terminal 106 is bent at the position exiting the resin package 107 to extend downward along the side surface 107a, 107b of the resin package 107 and bent at the lower end of the side surface toward the lower surface 107c. The end 105c of the anode terminal 105 and the end 106c of the cathode terminal 106, which extend along the lower surface 107c of the resin package 107, serve as mount portions.